The aims of this work are to study, in the very small related DNA phages S13 and phi X174, regulation of protein synthesis and control of the RNA-primed stage of DNA replication. Both the study of the control of messenger RNA synthesis and of the RNA involved in DNA synthesis will make use in part of cell strain with mutated RNA polymerases. The effects and properties of these mutated RNA polymerases will be studied. A study of transcription by normal polymerase will also be required and part of this work will aim to identify the phage-specific mRNA species. Another part of the work will involve localization of mutations in regulatory regions, i.e. in promoter sites and ribosome binding sites. DNA "protection" fragments bearing these mutated regulatory regions will be separated, sequenced and compared with the sequence of the wild-type regions. The role of helical structure of phage mRNA on regulatory of translation will be studied by carrying out in vitro protein synthesis with purified in vivo messenger under various RNA denaturing and degradative conditions. The requirement for RNA synthesis in replication of M13, S13 and phi X174 DNA will be studied in strains containing normal and mutated polymerases. A search will be made to see if any host protein factor confers RNA priming specificity on RNA polymerase. It is aimed to visualize in vitro transcription and translation in these phages by the method of Miller et al. (1970). Such EM pictures should give information on sizes of genes, intercistrons, and effects of polar mutants.